Library Coq.Numbers.Integer.Abstract.ZLcm

Least Common Multiple

Unlike other functions around, we will define lcm below instead of
axiomatizing it. Indeed, there is no "prior art" about lcm in the
standard library to be compliant with, and the generic definition
of lcm via gcd is quite reasonable.

By the way, we also state here some combined properties of div/mod
and quot/rem and gcd.